In Vitro Activity of Telithromycin, Quinupristin/Dalfopristin, Linezolid and Comparator Antimicrobial Agents Against Staphylococcus aureus Clinical Isolates

Abstract

We have studied the prevalence of the different macrolide, lincosamide, streptogramin_B (MLS_B) phenotypes among clinical Staphylococcus aureus isolates erythromycin- and/or oxacillin-resistant; and also the activity of other antimicrobial agents including telithromycin, quinupristin/dalfopristin, linezolid, aminoglycosides, chloramphenicol and vancomycin. We found that 64.86% of S. aureus were oxacillin-resistant. While the most prevalent MLS_B phenotype among methicillinresistant S. aureus (MRSA) was constitutive MLS_B (cMLS_B) (83%), among methicillin- susceptible S. aureus (MSSA) it was inducible MLSB (iMLS_B) (90%). Kanamycin resistance was more frequent than resistance to other aminoglycosides, being 100% for MRSA. Telithromycin was only active against iMLSB, MS and erythromycin- susceptible isolates, although resistance rates were found among iMLS_B MSSA (2.78%). Quinupristin/dalfopristin showed greater activity, with resistance rates of 2.5% for MRSA and 1.53% for MSSA. Both vancomycin and linezolid were fully active against all the isolates tested, with the highest MIC value being 2 μg/ml and 4 μg/ml, respectively. Among MRSA strains, 81.67% displayed resistance to five or more antimicrobials. This multiresistance was more frequently found among cMLS_B strains (96.38% MRSA resistant to 6-9 agents).

Keywords:

• Staphylococcus aureus
• telithromycin
• quinupristin/dalfopristin
• linezolid
• macrolides
• oxacillin resistance